1. Field of the Invention
This invention relates to the field of COMINT/ELINT (communications intelligence/electronic intelligence) signal processing, and more particularly to a circuit with which very low-level to moderate-level signals can be detected, without any a priori information, while other stronger signals are present and transmitting close to the instantaneous frequency of the desired signal.
2. Background Art
Reference is made to U.S. Pat. No. 4,965,581 entitled, "Real Time Rejection Circuit to Automatically Reject Multiple Interfering Hopping Signals While Passing A Lower Level Desired Signal" by W. Skudera & S. Albert, issued Oct. 23, 1990 (hereinafter "the '581 patent").
Reference is also made to a paper entitled "SAW Tapped Delay Lines for New Potential Circuit Applications" by William J. Skudera, Jr., which was published in approximately September 1988 in the Proceedings of the 42nd Annual Frequency Control Symposium 1988, IEEE Catalog No. 88CH2588-2, Library of Congress No. 58-60781 (hereinafter "the 1988 article"); and to U.S. Pat. No. 5,384,545, filed 17 Nov., 1992 in the name of William J. Skudera, Jr., titled "Sequential Circuitry for Recreating CW Components from Chirp-Z Pulses," and the 1988 article describe several embodiments of circuits which use a tapped delay line in an amplifier feedback loop circuit to replace the inverse transform of a chirped Fourier transform processor for CW input signals. The conventional inverse transform processor loses on the order of 20-30 dB of the processing gain achieved by the forward processor. However, the described circuit can be utilized to recirculate the signal in order to recreate a continuous CW signal from the transform signal.
In addition, reference is made to FIG. 2 of U.S. Pat. No. 5,355,091 filed May 21, 1992 in the names of Stuart D. Albert and William J. Skudera, Jr. entitled, "Apparatus and Method for Real Time Interference Signal Rejection" ('091 patent).
The disclosures of these and all other prior art materials referred to herein are expressly incorporated by reference.
Conventional methods have failed to achieve detection of very weak desired signals under adverse conditions and without a priori information about the received signals, because such detection requires a circuit with both ultra-wide dynamic range and very high signal sensitivity. The receiver must be able to receive moderate- to very-low-level signals without becoming saturated and therefore being made inoperable by the strong signals.